The long-term objective of this proposal is to understand the pathophysiology of autosomal dominant polycystic kidney disease (ADPKD) as a basis for rational therapy, including gene therapy, of the disease. Mutations in at least three genes cause ADPKD. PKD1, on chromosome 16, accounts for about 85% of cases. PKD2, a gene on chromosome 4, accounts for 15% of cases. PKD3 has not been identified. The DNA sequences of both PKD1 and PKD2 have recently been determined. PKD1 encodes a 4,304 amino-acid cell-membrane protein, "polycystin", that has a series of five adhesive extracellular domains, several membrane-spanning segments and a short cytoplasmic tail. PKD2 encodes a 968 residue protein containing six putative membrane-spanning segments with intracellular N- and C-termini. The overall aim of the proposal is to determine the biological role of PKD2 and the pathophysiology of PKD2-disease. Since, the only clue to PKD2 function is its homology with voltage activated Ca2+ and Na+ channels, the first aim of the proposal is to determine whether PKD2, the murine homologue of PKD2, encodes a channel. One of the most powerful new approaches for studying disease pathogenesis is targeted gene mutation. Standard transgenic technology results in insertion of the transgene at quasi-random sites in the genome so that the transgene and endogenous genes are simultaneously expressed. Gene targeting, by contrast, allows mutated sequence to be substituted for the allelic endogenous sequence so that the mutation can be studied in the context of the natural chromosomal (regulatory) environment. This technique will be used to create two mouse models of PKD2-disease, each containing a mutation that mimics a mutation found in man. Analysis of these models will have significant advantages over the study of pathogenesis directly in man. First, mouse tissues are available from all organs at all stages of development and can be used to study the spatial and temporal distribution of PKD2-protein. Second, mouse models can be used to study "modifiers", genes that affect disease severity. These results in mice will then be used to guide the search for modifier effects in human kindreds, a task which is almost impossible by conventional human genetic linkage analysis alone. Finally, in the longer term, mouse models will be used to develop new therapies and evaluate existing therapies for ADPKD to reduce the risk and expense of carrying out such studies in humans.